Abstract
Abstract Extraction of energy from tidal streams has the potential to impact on the morphodynamics of areas such as sub-tidal sandbanks via alteration of hydrodynamics. Marine sediment transport is forced by both wave and tidal currents. Past work on tidal stream turbine impacts has largely ignored the contribution of waves. Here, a fully coupled hydrodynamic, spectral wave and sediment transport model is used to assess the importance of including waves in simulations of turbine impact on seabed morphodynamics. Assessment of this is important due to the additional expense of including waves in simulations. Focus is given to a sandbank in the Inner Sound of the Pentland Firth. It is found that inclusion of wave action alters hydrodynamics, although extent of alteration is dependant of wave direction. Magnitude of sediment transport is increased when waves are included in the simulations and this has implications for morphological and volumetric changes. Volumetric changes are substantially increased when wave action is included: the impact of including waves is greater than the impact of including tidal stream turbines. Therefore it is recommended that at tidal turbine array sites exposed to large swell or wind-seas, waves should be considered for inclusion in simulations of physical impact.
Highlights
Tidal stream turbines (TSTs) are maturing as a means of renewable energy generation: several demonstration devices have been deployed and the world's first array will be installed in the Inner Sound of the Pentland Firth with the aim of 386 MW of installed capacity by 2020 [1]; [2]
These modules are fully coupled: that is, at every time-step currents and water depths for the spectral wave (SW) module are read from the HD module; radiation stresses from the SW module fed to the HD module; and wave and current forcing from both the HD and SW modules is used by the sand transport (ST) module to compute sediment transport and bed level changes
This study has investigated the impact of TST energy extraction on a sub-tidal sandbank in the Inner Sound of the Pentland Firth and focused on whether it is necessary to include waves in the simulation of TSTs and their impact on morphodynamics
Summary
Tidal stream turbines (TSTs) are maturing as a means of renewable energy generation: several demonstration devices have been deployed and the world's first array will be installed in the Inner Sound of the Pentland Firth with the aim of 386 MW of installed capacity by 2020 [1]; [2]. Presence of support structures and extraction of energy will impact a range of receptors, both physical [3e7] and biological [8e11]. This contribution simulates impact to the morphodynamics of sub-tidal sandbanks using a fully coupled wave e hydrodynamic - sediment transport model. This enables inclusion of wave driven sediment transport and wavecurrent interaction (WCI) in the computation. Sub-tidal sandbanks must be considered in environmental impact assessments because they can be important ecological habitats, navigational hazards and sources of aggregates. Tidal residuals may be reversed [21,22] both due to WCI and the dominance of wave driven currents
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